A low voltage alternating current electric field may be generated in a conductor layer by a long and narrow common electrode arranged around a capacitive touch screen. Upon a finger touching the screen, a coupling capacitor may be generated between the finger and the conductor layer due to an electric field of the human body, an electrical current may flow from the common electrode around the capacitive touch screen to the touch point, and the size of the current is in proportion to a distance between the finger and the common electrode. The proportion and the size of the current are calculated by a controller arranged behind the capacitive touch screen, so as to accurately determine a position of the touch point.
However, the capacitive touch screen is prone to shift due to a noise interference, which may be caused by a variation of ambient temperature, ambient humidity, and ambient electric field, and lead to an inaccurate determination of the position of the touch point. A significant portion of the noise interference on the capacitive touch screen is caused by a noise of a common electrode voltage (VCOM). In the related art, it is provided a VCOM filter circuit in a flexible printed circuit board (FPCB) for filtering the VCOM from a driver integrated chip (IC), so as to process the noise of the VCOM for the capacitive touch screen. The VCOM filter circuit is provided to filter the VCOM inputted by the driver IC included in the capacitive touch display device, and the filtered VCOM is provided to the common electrode arranged around the capacitive touch screen and included in the capacitive touch display device via an output end of the VCOM. However, such implementation of filtering the noise of the VCOM is not satisfactory because there is a wide frequency range of the noise of the VCOM interfering on the capacitive touch screen.